perfidy (noun) - the deliberate breaking of faith; betrayal of trust; treachery [pur-fi-dee]
BREAKDOWN: PER- (beyond) + FID- (faith) + -Y (state of)
perfidious means treacherous, disloyal, or unfaithful
“The best laid plot can injure its maker, and often a man's perfidy will rebound on himself.” —Jean De La Fontaine